Antacid Tablet Race
TOPIC: Rocket fuels and propellants
Objective: To demonstrate how increasing the surface area of
a chemical increases its reaction rate.
Description: A whole antacid tablet and a crushed tablet are
added to separate beakers of water so that their relative reaction rates
can be compared.
EDITED BY: Roger Storm, NASA Lewis Research Center
Materials:
- Antacid tablets (two per test)
- Two beakers (or glass or plastic jars)
- Tweezers or forceps
- Scrap paper
- Watch or clock with second hand
- Small block of wood
Procedure:
- Fill both beakers about half full with water of the same temperature.
- Wrap paper around one antacid tablet. Place the packet on a hard surface
and crush the tablet by pressing on it with the wood block.
- Open the paper packet with the crushed tablet and hold it over one
of the beakers. Pour the powder in the water and time how long it takes
for the powder to dissolve.
- Pick up a whole tablet and drop it into the second beaker of water.
Time how long it takes to dissolve completely.
Discussion: This activity demonstrates how increasing the surface
area of an antacid tablet by crushing it into a powder increases the rate
in which it dissolves in water. This is a similar situation to the way
the thrust of a rocket is increased by increasing the burning surface of
its propellants. Increasing the burning surface increases its burning rate
since more fuel becomes exposed to oxygen . In solid rockets, a hollow
core extending the length of the propellant will permit more propellant
to burn at a time. This increases the acceleration of the gases produced
as they leave the rocket engine. Liquid propellants are sprayed into the
combustion chamber of a liquid propellant rocket to increase their surface
area. Smaller droplets react more quickly than do large ones, increasing
the acceleration of the escaping gases.
Teaching Notes and Questions:
- This activity is an ideal way for safely showing how the burning rate
of rocket propellants is increased without having the students use fire.
- A similar activity can be tried with small pieces of hard candy. Take
two pieces of candy and crush one. Then, give the whole candy piece to
one student and the crushed candy to another student to dissolve in their
mouths. Which candy will dissolve first?
- Demonstrate the same effect by trying to ignite a thick piece of wood
with a match. Next, cut the wood with a sharp knife to make shavings. Then,
try to ignite the shavings. Caution: Be sure to exercise proper safety
precautions with fire.
EVOLUTION OF CARBON DIOXIDE LAB A chemistry lab
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